(a) Field of the Invention
The present invention relates to a single-lens reflex camera, and more particularly it concerns a real-time light-measuring system for a single-lens reflex camera having an image-pickup surface of a high reflectivity
(b) Description of the Prior Art
Conventional real-time light-measuring systems for single-lens reflex cameras are designed to measure, by a light-measuring device via a light-measuring optical system disposed outside the photographing light path, a light reflected from an image-pickup surface. This conventional system will be briefed hereunder by referring to FIG. 1. Reference numeral 1 represents a quick return mirror of a single-lens reflex camera; 2 a photographing lens; 3 an image-pickup surface; 4 a light-measuring optical system disposed on the outside of the photographing light path; and 5 a light-measuring device. The said system comprising the above-mentioned parts is constructed to insure that, among the lights reflected at the image-pickup surface 3, the illustrated reflection light A impinges onto the light-measuring device 5 via the light-measuring optical system 4. In such a case, it should be noted that, since the image-pickup surface 3 represents an emulsion surface of an Ag-salt film, it has a high light diffusibility, leading to the advantage that, even when both the light-measuring optical system 4 and the light-measuring device 5 are positioned outside the photographing light path, there can arrive an ample amount of light at the light-measuring device 5, and accordingly an adequate measurement of light can be achieved. However, in a single-lens reflex camera designed to perform image-pickup by means of an electronic image-pickup tube or a solid-state image-pickup device, it should be noted that the image-pickup surface of such a camera has a very high reflectivity, i.e. a low light diffusibility. Accordingly, in case both the light-measuring optical system 4 and the light-measuring device 5 are disposed outside the photographing light path as shown in FIG. 1, there can not arrive a sufficient amount of light at the light-measuring device 5. Thus, such a prior art light-measuring system has not been suitable for use as the real-time light-measuring system of a single-lens reflex camera which requires a specially high precision performance of light-measuring.